1. Field of the Invention
The present invention is related to ligands and complexes for homogeneous catalytic enantioselective hydrogenation. More particularly, the invention relates to ligands of formula (I) ##STR3##
Another aspect of the invention is related to complexes of formula (II), and to ##STR4##
a method for their preparation and use.
Enantioselective introduction of stereogenic centers into organic molecules by homogeneously catalyzed hydrogenation is established industrially for special applications. The enantioselective products are valuable starting substances for the production of biologically active agents.
2. Discussion of the Background
The use of catalysts containing bisphosphine ligands for enantioselective homogeneous catalytic hydrogenation for the above purposes is known (Burk et al., Tetrahedron, 1994, 4399).
Knochel et al. (Chem. Eur. J. 1988, 4, 950-968), Hayashi et al. (J. Chem. Soc., Chem. Commun. 1989, 495-496) and Ikeda et al. (Tetrahedron Lett. 1996, 4545-4448) describe Pd complexes with C.sub.2 symmetric ferrocenyl (bis-tert-phosphine) ligands. However, these complexes were used only in asymmetric allylations.
In contrast, Yamamoto et al. (Bull. Chem. Soc. Jpn. 1980, 53, 1132-1137) reported the use of non-C.sub.2 -symmetric ferrocenyl(bis-tert-phosphine) ligands in enantioselective homogeneous catalytic hydrogenation reactions. However, only very sporadically good enantiomer excesses are obtained with these ligands.
The basic suitability of non C.sub.2 symmetric ferrocenyl ligands for enantioselective hydrogenation is taught in WO 96/32400 and WO 95/21151.